Image and Graphics Colors

The number of colors used for displaying images and graphics is specified by the user. The colors used for displaying images are called image display levels. The colors used for displaying graphics are called graphics color levels.

In general, you don't need to know the specific image display level numbers. You do need to know the graphics color level numbers, because many commands require you to specify the output color by level number. For example, in the MAP command you specify a graphics color level number to pick the color of the map.

Each graphics color level is assigned a default color. For example, level 1 is assigned magenta. Graphics color level 0 has a special definition as the graphics background. You cannot draw graphics in level 0, but you can change it from the default color of black to a color of your choice for the background of the graphics you draw. Use the GU command to list and change the graphics color levels.

The number of colors used for displaying images and graphics depends on the number you request at startup and the number of colors available on your workstation. The maximum number of colors is 253 or 254, depending on your hardware.

The total of number of image display levels and graphics color levels cannot exceed the number of available colors (253 or 254). If you specify a total that exceeds the number of available colors, the workstation provides as many colors as possible. The more image display levels you request, the fewer colors there are available for graphics color levels and vice versa.

Use the -imageColors and -graphicsColors flags at startup or in your .mcidasrc file to specify the number of image display levels and graphics color levels in your McIDAS-X session. The default number of image display levels is 128. The default number of graphics color levels is 16 and the maximum is 128.

Because there are fewer image display levels (128 default, 254 maximum), than grayshades defined in most images (256), some image display levels are assigned multiple grayshades. For example, grayshades 0-16 may all be displayed as image display level 17. The SCALE ON and OFF options in the TERM command provide two methods of assigning grayshades to image display levels. See the TERM command in Chapter 3 for more information.